Temporal humidity variations in the heritage climate of South East England

Abstract

Humidity is an extremely important parameter in the protection of cultural heritage. Despite this its climatology has not been frequently studied. A range of instruments have been available for many years, but until recently accurate measurement has been problematic. Assessing average humidity has been difficult because of the wide diurnal and annual variation and the sensitivity of the water content of the air to temperature. Observations at Gatwick and Heathrow since the middle of the 20th century suggest a decrease in relative humidity, which may be as much as 10% in the summer months by the end of the 21st century. Estimates of salt damage and stress in wood, caused by day-to-day fluctuations in humidity for the rest of this century, are difficult to predict because increased dispersion in daily values. A careful analysis of the data structure suggests these pressures may be relative constant, such that salt weathering by halite is likely to be fairly constant through the coming century. However, the problems with the data structure indicated the danger in using sequential daily values from the UKCP09 projections. Indoors, taking the Cartoon Gallery at Knole near Sevenoaks as an example, suggests conditions will be reasonably constant over time. However, maintaining a lower indoor humidity close to 50% would likely involve the removal of much larger amounts of water during dehumidification in the future. © 2013 Brimblecombe; licensee Chemistry Central Ltd.